Interference eliminating apparatus for radio receivers



Nov. 15', 1938. R. E. WOOD 2,136,659

INTERFERENCE ELIMINATING APPARATUS FOR RADIO RECEIVERS Filed Nov. 18, 1935 4 Sheets-Sheet 1 R. E. WOOD Nov. 15, 1938.

INTERFERENCE ELIMINATING APPARATUS FOR RADIO RECEIVERS 1935 4 Sheets-Sheet 2 Filed Nov. 18

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Nov. 15, 1938. R. E. WOOD 2,136,659

INTERFERENCE ELIMINATING APPARATUS FOR RADIO RECEIVERS Filed Nov. 18, 1955 4 Sheets-Sheet 4 t 'IIIIIIII4 v r- 69 VIII/11110111411 75357277017475 Z/Z/5UU 2 13% I E M Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE INTERFERENCE ELIMINATING APPARATUS FOR RADIO RECEIVERS Application November 18, 1935, Serial No. 50,344

18 Claims.

My invention relates in general to the elimination of local electrical interference in a radio receiver, and particularly electrical interference in a radio receiver for mounting in an automobile, aircraft, or other like conveyance, and is an improvement over the invention of Patent No. 2,021,676.

Until the introduction of the interference eliminator of the Patent No. 2,021,676, it has been virtually impossible to remove high frequency interference from a radio receiver installed in an automobile, airplane or other conveyance powered by an internal combustion engine and having the usual ignition system. In the commercial form of the device of the above patent a separate lead is employed running from a metal medium carrying interference voltage to the interference eliminator unit itself to carry balancing interference voltage thereto. Although the device of this patent has attained marked success, I have found that there is occasionally some delay and difiiculty in finding a point on the automobile carrying electrical interference of the proper wave shape and phase, received by the main antenna for the radio receiver system.

It is an object of my present invention to provide an improved device for removing interference from a local source, in a radio receiver system.

A further object is to provide an improved device for eliminating ignition interference from a radio receiver system mounted on a mobile craft powered by an internal combustion engine.

It is also an object to provide a device, eliminating interference in a radio receiver system, which will provide more satisfactory interference elimination in a lower cost device, both from the standpoint of the manufacturing and installation cost of the radio receiver system as well as the device itself.

A still further object of my invention is to provide such a device in a sturdy compact form for mounting substantially in a unit, and removably, in the receiver chassis housing, in a position for simple connection into thereceiver system circuit.

One of the features of my invention is the provision of an interference eliminator unit for a radio receiver system for a mobile craft, for con nection between the radio receiver and signal antenna thereof, which unit utilizes the electrical interference in the circuit for the battery supplying direct current to the ignition system for the craft and to the radio receiver, to balance out similar interference received over the signal antenna.

A further feature is the provision of a simplified interference eliminator which utilizes a portion of the ordinary current conductor structure of the radio receiver system for a mobile craft, thus expediting the installation of the receiver, reducing the usual number of parts, and simplifying the servicing of the radio receiver.

Another feature is the provision of a movable shutter operating across an opening in the mounting member for the interference eliminator, between the two stationary coils of the balancing portion of the same, to vary the coupling between said coils.

A still further feature is the provision of a cast shielding and mounting member to carry the interference eliminator for preliminary assembly of the same, and then subsequent mounting in the receiver housing.

Other objects and advantages will be apparent from the following description taken with the drawings, in which:

Fig. 1 is a circuit diagram of the device of my invention in its preferred embodiment connected into a radio receiver system.

Fig. 2 is a modification of the circuit of Fig. 1.

Fig. 3 is another circuit modification illustrating in one diagram several possible circuit arrangements utilizing the device of my invention.

Fig. 4 is a circuit diagram illustrating the use of the balancing portion alone of the device and circuit of Fig. 1.

Fig. 5 is a diagrammatic representation of the most simple embodiment of my invention.

Fig. 6 is a complete circuit diagram of a commercial embodiment of my invention in a radio receiver, with the electrical system of an automobile on which the receiver is installed.

Fig. '7 is a bottom plan view in actual size of the removable mounting for carrying the interference eliminator unit as well as filtering structure for the supply leads to the receiver.

Fig. 8 is a sectional view along the line 8--8 of Fig. '7.

Fig. 9 is a fragmentary sectional View along the line 9-9 of Fig. 7.

Fig. 10 is a sectional view looking in the direction of the arrows along the line I0-l0 of Fig. 7.

Fig. 11 is a fragmentary cross sectional view along the line I l-l l of Fig. 7.

Fig. 12 is a fragmentary cross sectional view along the line l2l2 of Fig. '7.

Fig. 13 is a fragmentary sectional view along the line l3-l3 of Fig. 7.

Fig. 14 is a top plan view of the complete cast housing and mounting member for the interference eliminator in position in the receiver housing, which latter is illustrated in a fragmentary portion.

Fig. is a cross sectional view along the line |5I5 of Fig. 14.

Fig. 16 is an end view of the structure of Fig. 14, showing the receptacle portion for making connection to the external units of the receiver system, and the antenna and current supply leads extending into the housing.

In practicing my invention I provide a unit comprising primary and secondary inductance coils connected in series with a filter portion consisting of one or more inductances and corresponding condensers, which filter portion in turn is connected to the input impedance of a radio receiver. The signal antenna for the receiver system is connected to the secondary inductance coil, and the A supply lead for the radio receiver is preferably connected in series, with the primary coil in the balancer portion of the unit, but said lead may be connected in parallel with the primary coil. This structure is supported in a two-piece shielding and mounting device which also carries supply lead filters, and the device is mounted in the receiver housing itself, but separately from the receiver chassis. The interference eliminator may also be constructed and installed on the vehicle as a separate shielded unit and connected into the receiver system as previously described.

High frequency electrical interference from the ignition system has been the most serious problem to overcome for successful operation of a radio receiver installed on such craft as an automobile, airplane, boat and the like. Until the introduction of the device of the above noted patent, or unless considerable sensitivity in the receiver was sacrificed, it was necessary to employ suppressors on the spark plugs of the engine of the craft and on the distributor, bond various points in the craft structure, and employ miscellaneous filters at points in the receiver system. The introduction of the prior device, however, eliminated the necessity of much of this equipment and particularly the suppressors, which suppressors acted to reduce the operating motor speed of the mobile craft. with the previous device, as mentioned above, considerable time was sometimes required to locate a point on a metal medium carrying interference voltage of correct wave shape and of a phase so that it could be fed to the unit to act upon like interference voltage received over the main antenna of the radio receiver system.

In the present invention, however, this interference voltage in the signal antenna is supplied to my unit with the A power supply to the radio receiver. Inasmuch as the A battery for the radio receiver system is also the. battery supply for the ignition system of the mobile craft, the same ignition interference voltage as radiates to the signal antenna of the receiver system is car ried with the A power supply for the receiver. These interference currents are of exactly the same wave shape, and of such a phase and intensity as compared with the interference received by the main antenna, as to make balancing possible. Mobile craft employing ignition systems vary widely in design and as a result the ignition currents flowing through the metal parts of the craft, and the ignition interference voltage existing in the metal parts in the form of standing waves, vary in phase and wave shape with the variations in design of the mobile craft However,

itself, but, as mentioned above, the wave shape of the interference voltage in the battery connections is the same as that which would be radiated from the ignition system to a signal antenna of a radio receiver installed on a particular craft.

My device for removing interference, shown in the circuit diagram of Fig. l and in its physical structure in Fig. 7, comprises a primary inductance coil l0 and a secondary inductance coil H with an interposed electrostatic shield l2 connected to ground. The balancer portion is shielded from a filter portion including an inductance coil [4 in series therewith, and a shunt condenser IS in the circuit with the inductance coil M. A second similar filter portion is provided with an inductance coil I1 and a shunt condenser !8, although the latter may be left out as shown in the circuit of Fig. 6. An isolating condenser H of negligible impedance is also included in the circuit ahead of the secondary inductance coil II. This condenser is employed so that if a low resistance short to ground develops in the antenna system, it prevents the short from disturbing the A. V. C. or automatic volume control network. The double helix type inductance coil as disclosed in Patent No. 2,021,676 is a very satisfactory and inexpensive structure for the present device. It is understood, however, that I may employ other types of inductance coils than that specified above. As an example of the constants for the above members, in one circuit I have used a primary of 1.16 microhenries, a secondary of like inductance, although this could vary 2% either way, and coils l4 and I! of 2.5 microhenries. These might vary 10% either way. In this example the condenser l6 was 400 micro-microfarads, and the condenser [8 was 200. The termination of the. filter in the circuit of Fig. l is the A. V. C. by-pass or trimmer condenser which is preferably mounted with the interference eliminator as a whole as shown in Fig. '7. The capacity of this condenser may vary quite widely and range from 50 to 800 micro-microfarads as desired. An adjusting screw 2| extends through the mounting and main housing as shown in Fig. 16. This type of termination offers marked advantages from the standpoint of ignition frequencies in that it provides a decreasing impedance with increasing frequency. Since ignition frequencies are largely of a higher order than broadcast frequencies, this type of termina tion presents a low impedance path to ground to these higher order ignition frequencies.

Connection between the filter portion and the first R. F. stage of the receiver is effected by a lead 59 or, as in the commercial embodiment, by a jack connection. An inductance 22 and A. V. C. resistance 23 are provided in the first R. F. stage. The first resonant circuit capacitance is indicated by reference character 24 and the tube of this stage by the reference charac ter 26.

In the embodiment of Fig. l the objectionable interference energy is intercepted by a signal antenna 1' which is connected with the secondary ll of the balancing portion through a shielded lead 25, and a lead 28 carries the A supply to the radio receiver through the primary I!) of the balancing unit. The lead 28 may be shielded, but is not necessarily so constructed. Interference voltage from the ignition system is present in the storage battery circuit, which circuit is common to the ignition system and radio receiver system,

and the interference is therefore fed through the A supply lead to the balancing unit for balancing out like interference received through the signal antenna 21. In this embodiment the lead 28 ordinarily does not go directly to the car battery because of the time and trouble necessary to the installation, but, for convenience, it goes to a wire of the battery system such as a lead coming from the A battery to the ignition switch (Fig. 6) of the automobile. Furthermore, there is less interference energy at the battery terminals themselves than at the other connections indicated, which less amount of energy would necessitate larger balancer coils. The A supply to the receiver, after going through the primary coil ID of the balancing unit, is carried through a filter including one or more (Fig. 3) inductances 29, and by-pass condensers 3| through lead 32 to the filament 33 of the first tube and other succeeding tubes of the radio receiver. In the circuit cited above simply as one example of the invention, the capacity of the condensers 3| ranged from 450 to 630 micro-micro-iarads, while the inductance values over the four supply and control leads, as will be described, varied from one microhenry in the A lead to approximately '75 in the tone control lead on the right side. A balancing terminating condenser 30 is connected in shunt with the lead from the primary as shown in Fig. 1. In the commercial embodiment of my invention the balancing and filter unit is mounted in shielded compartments provided in a cast member removably carried in the main housing for the radio receiver, but separated from the receiver chassis itself. This separate mounting and shielding member shown in detail in Figs. 7, 14, 15 and 16 in the diagrammatic representation of shielding which is indicated by reference character 34, carries a terminal'strip for the other supply leads to the radio receiver, and external units of the system, with the terminals including a voice coil terminal 36, a field coil terminal 31, both going to the speaker for the radio receiver, and a dial light terminal 38 as well as a tone control terminal 39 extending to the control head for the radio receiver.

Fig. 2 illustrates a modified circuit for my in vention in which the balancing and filter structure is supplied with balancing interference volt age by a parallel or shunt circuit including a lead 4! extending from an A terminal connection 42 on the mounting member directly to the primary IQ of the balancing unit. A blocking condenser 43 is inserted in this line to prevent the A supply to the radio receiver from short circuiting through the balancing unit. That is, the condenser 43 of low impedance, will pass only alternating currents, and blocks off the direct current in the A supply so that only the high frequency interference voltage (A. C.) is carried in through lead 4! to the balancing unit from the A supply. A resistance may be substituted for the condenser 43 if so desired. The A supply to the filament of the tube of the receiver then passes through a supply lead filter including inductances 29 and by-pass condensers 3| as described in connection with Fig. 1. If desired, a small mica shunt condenser 48 may also be employed. Only one of these condensers is shown in Fig. 7, but the other leads are broken to indicate where they may be inserted. As previously stated, these elements may be varied in number and value in accordance with the requirements of the circuit in question. A terminal strip similar to that shown in Fig. 1 may be mounted on the mounting and shielding member 34 for the balancing and filter unit and utilized with this circuit as previously described.

The interference voltage for use in balancing out similar interference voltage received through the signal antenna 2'! in addition to being brought in as shown in Figs. 1 and 2, may also be introduced into the balancing portion (as shown in Fig. 3), through a parallel or shunt circuit in cluding either the speaker field terminal 31, or dial light terminal 38 which both receive direct current. The diagrammatic illustration of Fig. 3 shows the balancing and filter portions of the structure of Figs. 1 and 2. However, the primary coil Iii may be out into the line or connected to the lead from either terminal 31 or terminal 38. When the coil to is connected as illustrated in full lines, a connection is also effected between terminals 37 and 31, and 38 and 38', and when out in at either of these positions a jumper is used from A2 to complete the circuit. In any position the balancing comes before any filtering action, inasmuch as the balancing energy must be brought into the primary coil it] pure. The filters shown outside terminals 3i and 3B prevent interference from getting to the antenna, and also prevent free radiation from getting into the set.

Fig. 4 illustrates the balancing portion of the unit alone, employing the primary coil H), a secondary coil H, and the interposed electrostatic shield l2. If the balancing portion alone is employed for removing interference received over the signal antenna, it may be connected into the radio receiver system with the A supply lead 23 connected to the primary coil, and the signal antenna 2"! connected to the secondary as shown in Fig. l. A lead I! extends from the secondary coil to the first E. F. stage of the radio receiver, with a capacitance it in shunt therewith. The A supply is carried to the set through lead 15 with condenser E! in shunt therewith, and through the filter indicated in Fig. l.

The simplest embodiment of my invention is illustrated diagrammatically in Fig. 5. The A lead 28 to the radio receiver is wrapped tightly in one or more loops around the shielding 25 on the antenna lead 25 from the antenna 21'. The normal shielding 25 on a wire cable is open enough and as a result suificiently ineflicient so that the necessary electrical coupling is accomplished between the A lead and the antenna lead. Instead of wrapping the lead 28 around the shielding 25', the former may be laid parallel to the lead 25 and bound to the shielding 25 to eiiect the necessary coupling. In this embodiment the interference voltage from the ignition system in the A lead inductively opposes similar interference in the antenna lead. The phase of the induced current in the antenna lead 25 must be 186 from the interference in the lead coming from the antenna. In order to get this proper phase relationship in the two currents, the lead 28 may be wrapped in either one direction or the other around the antenna lead, depending on the phase of the interference in said lead 28. Likewise, if lead '28 is laid parallel to lead 25 the positioning of the former will bring about the proper phase relationship.

To illustrate the complete circuit of the radio receiver, the balancing and filter device, as illustrated in Figs. 1 and 7, and the ignition system of the vehicle, as an automobile for instance, upon which the receiver is mounted, I have shown in Fig. 6 a diagrammatic representation of these various circuits of a commercial embodiment of my invention. The radio receiver circuit includes the first resonant circuit or R. F. stage 26, a first detector 49, the intermediate frequency stage 5|, second detector and first audio 52, the second audio stage 53, and the output 54 from the receiver. A switch 50 is indicated in the power supply line, and the heaters or filaments 60 are shown for convenience removed from the tubes and in the A supply line. An ordinary storage battery 56 supplies direct current to the ignition system of the automobile, aircraft, or other mobile craft upon which the receiver is mounted, and also provides power for the receiver as previously described.

The interference voltage for the balancing portion of the device is carried in through the same lead 28 which supplies direct current to the radio receiver. The balancing and filter device, illustrated diagrammatically as surrounded by shielding in the preferred embodiment, is mounted on a single shielding and mounting member as shown in Fig. '7, and employs the inductance coils I0 and II as the primary and secondary respectively, in the balancing portion of the device, and two shunt condensers as I6 and I8 of Fig. l, and two inductances I4 and I 'I in the filter portion of the device. The lead 59 extends from the output of the filter to the first resonant circuit of the radio receiver. For convenience in illustrating the circuit on the drawings, the balancing and filter unit are shown separated from the filters in the supply and control leads, with a connecting lead 15 from one to the other. It is understood, however, that this is preferably to be carried in a single housing as shown in Fig. 7.

So far as the ignition system of the automobile is concerned, this includes, as stated, the battery 58, a generator GI, an ignition switch 62 to open and close the circuit to the ignition coil 63 and distributor 64. The breaker points are illustrated diagrammatically at 66, and a filter unit 5'! is shown in a shielding container 68 between the breaker points and ignition coil. It has been found in some installations that very troublesome interference voltage emanates from the breaker points, and the filter 61 is interposed in the line to substantially remove this particular interference. The filter Bl includes an inductance G9 and capacitance ll connected to ground. This filter is provided in its commercial embodiment as a complete unit and is quickly installed at the point indicated when necessary.

To further identify the parts of the radio receiver and circuit, the vibrator unit is designated by the reference character I2, and said vibrator is connected to a power transformer I3 supplying plate voltage to the radio receiver. A terminal strip 14 is designated in the shielding and mounting housing with terminal connections 36, 37, 38 and 39 corresponding to the illustration of Fig. l. The lead 15 is not external of the shielding housing 34, but is the same as indicated in Fig. l by the same reference character.

Structural description The physical structure of the balancing and filter device as well as the mounting therefor is illustrated in Figs. 7 to 15. Although a sheet metal stamping with assembled sheet metal walls to form individual shielded compartments for the elements of my balancing and filter device can be used, I preferably employ a mounting and shielding housing 34 comprising a one-piece seamless cast metal base 8| upon which to mount the elements as shown in Fig. 'l, with a one-piece seamless cast cover 82 securely bolted, or otherwise fastened onto said base. The base is divided up into a plurality of shielding compartments by integral walls as shown especially in Figs. 7 and 8. The two inductance coils I0 and II in their insulating casings stand vertical on each side of an integral partition or wall 83 having an opening 84 therein of substantially the same width as the wire coils themselves. The inductance coils themselves, either in a single coiled layer or in a single wire double layer winding as described in Patent No. 2,021,676, are each mounted, as shown best in Fig. 12, in a shallow cup insulating casing 86 with a removable insulating cover 81 which is held in position by an eyelet 88 or other fastening means which extends through to an insulating mounting plate 89. A fiber washer 9| may be inserted between the mounting plate and cover as shown in Fig. 12, and the plate slipped into a pair of oppositely disposed vertical channels 92 in a metal bracket 83 riveted or otherwise secured to the base 8|.

Inasmuch as the intensity of the interference voltage fed into the balancing portion through the A supply lead 28, and that received over the antenna lead 25, may vary in different installations, I provide an adjustable means for varying the coupling between the primary and secondary of the balancing portion to bring the intensity of the interference voltage induced in the secondary from the primary to substantially the same intensity as the interference energy in said secondary intercepted by the antenna. This is accomplished by a metal plate 96 (Fig. 12) serving as a shutter to vary the effective size of the opening 84 between the two balancing coils. The shutter is provided with a bracket in integral therewith and extending at right angles thereto, with an outwardly extending threaded collar 98 for receiving an adjusting screw 99. The adjusting screw is rotatably carried by a stationary bracket IOI riveted to the base BI and retained therein by a cotter pin I02 so that as the screw is turned at its head I03, the shutter moves back and forth axially thereof. screw lies adjacent an opening I04 (Fig. 16) in the outer housing I05 for the radio receiver to make it readily available for any adjustment desired.

It is desirable to maintain a positive ground connection between the shutter and the cast base or housing member 8I. To accomplish this ground connection and at the same time furnish a guideway for the shutter 96, I provide corresponding split finger wipers I06 on the base and I01 on the cover 82, which fingers are bent to resiliently press against the shutter and at the same time maintain the shutter in positive engagement with the partition 83. The pressure is such as to permit longitudinal movement of the shutter in response to the movement of the screw. Inasmuch as the ground connection for the shutter might not be absolutely perfect, there may be a small amount of interference set up in the shutter to be radiated to the balancer portion. If this should occur, the interference radiated would have less efiect on the balancing operation with the shutter in the compartment with the primary coil I0 which is the preferred mounting as shown in Fig. 7. The cover 82 is cast to provide partitions corresponding to those in the base BI so as to fit onto the base in the manner shown in Fig. 15 in a very tight shielding housing. The cover is just deep enough to clear the balancing coils and capacitances as shown in Fig. 8 and is pro- The head I03 of the III vided with apertures I08 which correspond to like apertures I09 in the base 8I. Self-tapping screws III are inserted in the aperture I08 to extend into the aperture I09, and a recess I I2 is provided in the cover so that the heads of the screws may lie below.the surface of said cover. With the large number of screws I II employed, a very tight connection is provided between the cover and base.

Providing a movable metal shutter over an opening between the inductance coils I0 and II, as described above, instead of moving one coil with respect to the other as has been done in the structure of Patent No. 2,021,676, has been found to materially increase the balancing efficiency. The inductance values of the coils Ill and II are very small, so small in fact that there might possibly be only a slight difference over the inductance value of a lead long enough to permit the movement of one of the two coils to vary the coupling thereof. A lead long enough to permit movement of an adjustable coil may also take various positions as the coil is adjusted, and with such a lead introducing a large inductance value into the circuit and twisting or the like, phase variations might be introduced to interfere with balancing. Using the shutter to vary the coupling, and maintaining the coils fixed with only a short lead, overcomes these difficulties.

An electrostatic shield assembly I2 is mounted in the base 8| on the side of the opening 84 opposite to the shutter 95. The shield assembly comprises a metallic plate I00 preferably having a plurality of slit fingers twisted over their length to insulatingly separate the fingers and lying parallel as shown in Patent No. 2,047,159, with a mounting portion at right angles thereto bolted or otherwise rigidly secured and grounded to the base as shown in Fig. 12. The shield I00 is covered with an insulating paper IIU which covers the top surface of the mounting portion of the shield and extends over the top of the fingers and down the back.

The inductance coil assemblies I4 and I! of the filter portion of my device are of a construction similar to that of the inductance coil assemblies of the balancing portion. However, the insulating housing for each coil assembly is slightly different in that outstanding ears H3 are provided on the shallow insulating cup 86 to correspond with integral abutments 4 (Fig. 9) with a pin H5 or the like used to secure the complete coil assembly to the base. A pin I I6 of insulating material extends through the inductance coil assembly and has washers or knobs on each end toretain the cup 85 and cover 8"! in position. The shunt condensers, such as I6 and I8 of the filter portion, are each of similar construction, and may utilize the surface of the base 8| as one plate while a metal plate III with an intervening dielectric member II8 provides the other plate for the condenser. These may be riveted to the base 8I as shown in Fig. 9. The value of these condensers may of course be increased by using a multi-plate condenser.

To effect a connection between the coils I4 and Il without an intervening inductance, the capacitance as I8 may extend from one compartment to the other (Fig. 8). The other walls defining compartments in the base are preferably cast integral with the base, but between these two particular compartments I provide a removable metal plate I2I for a shielding wall which may be inserted between the two posts I22 defining an opening between the compartments and secured in position by a bracket I23 extending at right angles to the plate after the condensers have been assembled. The bracket l23 may be integral with plate I'Zi and riveted or otherwise secured to the base.

Capacitances, indicated generally by 3I, as inserted in shun-t connection in the circuit of Fig. 1 between the primary coil and the filament of the first tube of the receiver in the A supply connection to the receiver, comprise an elongated central metal plate I24- with pieces of dielectric I26 on each side, and metal plates I2l on the outside the dielectric members. The center plate extends downwardly as shown in Fig. 10, below the other members to fit in a split stud I28 which in turn is bolted to the bottom of the base. This construction for he condensers provides two independent capacitances for each assembly and furthermore provides an inexpensive yet extremely sturdy assembly which may be readily mounted within the housing and mounting memher. 8 I, and is important electrically in addition to the natural function, in that one plate is used as aconductor as between connections to the receptacle E35 and inductance 29 for instance. When using a plate as a conductor for the energy to be filtered, better filtering action hasbeen obtained. Although the capacitance is indicated generally by reference character 3I, to more readily compare Figs. 1 and 7 I- have indicated the individual capacitances in the supply and control leads by 35a, Slb, Me and 3501. The condenser extends above the edge of the base BI, but thisis taken care of in the shallow cover 82 secured to the base.

An air core inductance 29 is also included in the A supply lead to thereceiver chassis.

Installation and operation In the installation of the complete radio receiver system on an automobile, airplane or the like, the shielding and mounting housing 34 is positioned in the bottom of the main radio receiver housing I05 as shown in. Figs. 14 to 16.

The cover 82 lies against the bottom of the housing or at the back, depending upon the position in ,45

which the complete radio receiver is installed, whilethe mounting portion designated as the base 8i has the closed surface facing upwardly into the housing, with jack connections I29 and I3I in separate terminal strips facing upwardly to fit :50

into corresponding sockets and terminal strips on the receiver chassis itself. A collar member I32 (Fig. 15) secured to the base BI and fitting around the aperture for the supply lead 28, a

similar collar I33 similarly mounted around the shield for the antenna lead 25, as well as a frame I34 around the external lead receptacle I35, face against the inside surface of the housing member, and in the case of collars I32 and I33, are pulled tightly against said inside surfaceby a screw I36 (Fig. 16) extending through the outer housing and into the base 8 I. Frame I34 extends through a corresponding aperture in the housing to lie flush with the outside surface of said housing.

This mounting substantially prevents any leakin a manner so that the electrical circuits of the system are completed through the connections including prongs I29 and I3I. A cover may then be fastened onto the housing I05 in the usual manner. With the electrical circuit connected, the shutter 96 is closed so that only the filter portion, including the inductance coils I4 and IT, is effective. With the intensity of the interference energy in excess of the capability of the filter, the shutter is adjusted to accomplish a coupling between the balancing coils so that the balancer portion operates in conjunction with the filter to substantially eliminate the interference energy in the antenna circuit. This setting for the shutter then remains constant during the life and operation of the radio receiver on that particular installation. If necessary for a more sat isfactory elimination of interference and operation of the radio receiver, a filter unit 61 as illustrated in Fig. 5 is connected into the ignition system between the ignition coil 63 and breaker points 66.

With the radio receiver turned on in the usual manner, the A supply is brought in through the lead 28 which also carries interference voltage from the ignition system of the craft on which the installation is made. Similar interference together with signal energy is brought into the secondary coil II through the lead 25 from the antenna 21 mounted as described on the vehicle. Since the ignition interference picked up by the antenna 2! radiates from the same source as the interference carried by the A lead and from which the balancer portion derives its balancing energy, the ratio between the intensity of the interference in the antenna and that in the A lead will automatically be substantially the same for all vehicles. If this interference coming into the primary through the A lead is 180 out of phase with that brought in from the antenna to the secondary, this condition may be corrected by reversing the connections to the primary or to the secondary so as to bring the interference to the same phase.

With the coupling between the primary and secondary coils of the proper value as determined by the original adjustment of the shutter, the interference brought into the primary coil induces a current in the secondary coil of the balancing portion of opposite phase to oppose the interference received in the antenna. Any high frequency interference remaining in the circuit is then filtered out in the filter portion including the two inductance coils I4 and I1, and is there substantially removed before the signal energy is fed into the radio receiver itself.

The A supply for the radio receiver circuit passes from the primary coil of the balancer portion over a lead having filtering structure such as the balancer terminating condenser 30 and the inductance 29 and capacitance 3Ia which in themselves form a filter. This filtering structure removes the interference which originally was brought in with the A supply to the set, and which interference induced the current in the secondary which was used to balance out the interference received over the antenna. The filter structure also removes any stray interference which might come in over the A lead so that it will not get into the radio receiver. However, such stray interference is not so likely to be present in the A lead as it is in the other supply leads and the control leads such as the dial light, speaker field, voice coil and tone control leads, where similar filters such as indicated generally by capacitances 3I and 48 and inductance 41 remove the stray interference and prevent it from getting into the set. These filters affect only the interference coming in over these leads and not that which comes into the radio receiver through the signal antenna.

With the current supply lead 28 connected to the interference eliminating device as illustrated in Fig. 2, the installation and operation are substantially the same as that described above, except that only the high frequency interference voltage is carried to the primary coil I!) through a lead ll while the direct current supply for the radio receiver is carried in over the lead including filtering structure as heretofore described.

In the present invention I have provided, therefore, a compact, sturdy removable housing for carrying in general the interference eliminating structure for a radio receiver system mounted on an automobile or the like. The invention is more particularly directed to the interference eliminator as embodied in the balancing and filter portions described, and as disclosed has resulted in standardizing the radio receiver installation by relying only on one specific balancing interference supply. Because the phase of the interference used for balancing is the same as that r ceived in the antenna, and the wave shape is substantially the same, the present invention eliminates phase and wave shape error with a resulting increased balancer efficiency. Furthermore, the number of external leads is reduced, and the overall cost of manufacture has been found to be reduced over the devices of the prior art.

Although I have described and illustrated my invention in its preferred embodiments, it is understood that I do not limit the invention thereby, but am limited only by the scope of the appended claims.

I claim:

1. A radio receiving system including an antenna circuit, a translating portion for translating the signal energy in said antenna circuit, a power supply lead for said translating portion, means for preventing interference effects in said translating portion from sources to which said power supply lead is connected, said means including a primary inductance coil connected to said power supply lead in a circuit including said lead, said coil, and a condenser in series, said lead also being connected through a filter inductance to said translating portion, a secondary coil inductively coupled to said primary coil and connected in series in the antenna circuit in such a manner that interference entering the system through said power supply lead opposes the interference energy in said antenna circuit.

2. Means for eliminating interference effects in an antenna circuit of a radio receiver and for supplying power to said receiver, including primary and secondary inductively coupled balancing coils suitable for connection of the secondary coil in the antenna circuit, a condenser, a filtering inductance, and a power supply lead, said power supply lead, primary coil and condenser being connected in series in one current path, and said supply lead and filter inductance being connected in series in another current path whereby the power current flows through said filter inductance and the interference currents flow through said primary coil.

3. In a radio receiver system, a radio receiver, a main shielding housing therefor, interference eliminating apparatus for said radio receiver, and a heavy rigid shielding housing therefor for removable mounting in said main shielding housing and separable from said radio receiver, said interference eliminating apparatus comprising a balancer portion having primary and secondary coils inductively coupled, and a shiitable conductor therebetween for varying the inductive relation of said coils, a plurality of filters including condensers two of which are formed by a central conductor plate rigidly upstanding from and within said rigid housing and outer plates on both sides of said central plate and separated therefrom by dielectric members; said central plate and said shiitable conductor both being grounded to said rigid housing, and said rigid housing being grounded to and with said main housing.

t. A radio receiver system for a mobile craft having an ignition system and a battery to supply direct current for said ignition system and for the radio receiver of said receiver system, an antenna circuit for said radio receiver, a direct current supply circuit for said receiver with a portion of each of said circuits inductively coupled, an apertured wall between said coupled portions, and means for varying the inductive coupling between said portions at the aperture in the wall, said means including a metal plate slidably supported against said wall, and an elongated screw threadably carried by said plate and rotatable to move said plate longitudinally across said aperture, and an electrostatic shield between one of said coupled portions and said plate.

5. A radio receiver system for a mobile craft having an ignition system and a battery to supply direct current for said ignition system and for the radio receiver of said receiver system, an antenna circuit for said radio receiver, a direct current supply circuit for said receiver with a portion of each of said circuits inductively coupled, an apertured wall between said coupled portions, and means for varying the inductive coupling between said portions at the aperture in the wall, said means including a metal plate slidably supported against said wall, a plurality of resilient metal wipers pressing against said plate to maintain said plate in engagement with said wall, and an elongate-d screw threadably carried by said plate and rotatable to move said plate longitudinally across said aperture, and an electrostatic shield between one of said coupled portions and said plate.

6. A radio receiver system for a mobile craft having an ignition system and a battery to supply direct current for said ignition system and for the radio receiver of said receiver system, an antenna'circuit for said radio receiver, a direct current supply circuit for said receiver, with a portion of each of said circuits inductively coupled, an apertured wall between said coupled portions, and means for varying the inductive coupling between said portions at the aperture in the wall, said means including a metal plate slidably supported against said wall and having an extension at right angles thereto, an elongated screw rotatably and threadably secured in said'extension to move said plate longitudinally of said screw across said aperture upon rotation thereof, and resilient means for pressing said plate against said wall to maintain contact therewith but permit longitudinal movement of the radio receiver of said'receiver system, an antenna circuit for said radio receiver, a direct current supply circuit for said receiver with a portion of each of said circuits spaced apart and inductively coupled, means for varying the coupling between said portions, including a movable metal shielding plate to vary the effective open space between said portions, and an electrostatic shield between said plate and one of said portions at said open space including a plurality of bars twisted to lie in planes parallel to one another and at an angle to the plane of said plate, with each of said bars insulatingly separated from an adjacent bar over the twisted portions thereof.

8. A radio receiver system including a radio receiver having tubes including heater elements therein, an antenna circuit for supplying desired signal energy to said radio receiver and also acting to pick up undesired signal energy, a battery for supplying low voltage direct current to said radio receiver, and means for substantially removing said undesired signal energy received over said antenna, said means including in combination balancing means comprising a pair of coils variably inductively coupled together with one of said coils connected with said antenna circuit and the other of said coils connected with said heater elements of the tubes, a lead from said battery circuit to said other coil having no intervening impedances therein to carry direct current for said heater elements and simultaneously carry to said other coil undesired signal energy of substantially the same wave shape and phase as that in the antenna circuit to inductively balance out said antenna undesirable energy, and a filter section intermediate said first coil in said balancing means and said radio receiver.

9. A radio receiver system for a mobile craft having an ignition system and a battery to supply direct current for said ignition system and for the radio receiver of said receiver system, said radio receiver having a filament circuit therein, an antenna circuit for said receiver acting to pick up desirable and undesirable signal impulses, a coil in said antenna circuit, a second coil inductively coupled to said first coil and in series connection with said filament circuit, and a single lead in connection with said battery to supply direct current to said second coil to be fed to said filament circuit and to simultaneously supply to said second coil undesirable signal impulses substantially the same as those picked up by said antenna and unaltered in wave shape in the passage to said second coil from said battery connection, and an electrostatic shield between said coils.

10. A radio receiver system for a mobile craft having an ignition system and a battery to supply direct current for said ignition system and for the radio receiver of said receiver system, said radio receiver having a filament circuit therein, an antenna circuit for said receiver acting to pick up desirable and undesirable signal impulses, a coil in said antenna circuit, a second coil inductively coupled to said first coil and in electrical connection with said filament circuit, a single lead in connection with said battery to supply direct current to said second coil to be fed to said filament circuit and to simultaneously supply to said second coil undesirable signal impulses substantially the same as those picked up by said antenna and unaltered in wave shape in the passage to said second coil, means for varying the inductive coupling between said coils, and an electrostatic shield intermediate said coils.

11. A radio receiver system deriving its direct current supply from a storage battery, said system including a radio receiver, an antenna picking up desired signals and also undesired signals from a source common to said storage battery, with said antenna connected to said radio receiver through an inductance coil, radio tubes for said receiver, each having a heater element therein, a second inductance coil in connection with the circuit of the heater elements and inductively coupled with said first inductance coil, a single lead in connection with said battery circuit and extending directly to said second inductance coil to feed direct current to and through said coil for said heater elements and to simultaneously feed in unaltered wave shape undesirable signal impulses to inductively balance out in said first inductance coil undesirable signal impulses from said antenna of the same wave shape and phase, means for varying the coupling between said coils, and an electrostatic shield intermediate said coils.

12. The combination of a power supply system including a storage battery radiating undesirable signal impulses, a radio receiver having an antenna circuit picking up desirable signal impulses and said undesirable signal impulses, and a translating portion, with the latter portion including a plurality of tubes having heater elements therein, inductive balancing means including a secondary coil connected in said antenna circuit before said translating portion, a primary coil in connection with the circuit of said heater elements, and a single impedance free conductor from the storage battery circuit directly to said primary coil to feed direct current and undesirable signal impulses to said primary coil with said coils inductively coupled in such a manner for said power-lead-undesirablesignal-impulses to inductively balance out similar antenna-circuitundesirable-signal-impulses, whereby the desirable signal impulses pass to said translating portion and said direct current passes to said heater elements.

13. In a radio receiver system for a mobile craft having an ignition system including a battery, a radio receiver circuit including a plurality of tubes having filament elements therein, a signal antenna for said circuit, with said battery for said ignition system supplying direct current for the radio receiver, means for eliminating undesirable signal impulses picked up by said antenna to be fed to the radio receiver including a pair of variably and inductively coupled coils, one of said coils connected between said antenna and the receiver circuit, and the other coil in electrical connection with said tube filaments, and a single lead connected from the battery to said other coil free of any impedance therein to carry direct current from said battery to the filaments of said tubes through said coil and simultaneously over the same single lead carry undesirable signal impulses of the same wave shape and phase as those picked up by said antenna to said other coil in such a manner as to reverse the phase thereof to inductively balance out said undesirable impulses in the antenna, and an electrostatic shield between the two coils,

14. In a radio receiver system mounted on an automobile having an ignition system including a source of direct current common to said radio receiver system, a receiver circuit including a plurality of tubes each having a filament therein heated by direct current, an antenna system for said receiver circuit and means for balancing out high frequency interference picked up by said antenna system from said ignition system, said means comprising balancing apparatus including an inductance coil in series with the antenna, a second inductance coil inductively coupled with said first inductance coil, and a lead from said source of direct current connected to said second inductance coil to carry direct current and high frequency interference thereto without any electrical interruption to inductively balance out in said balancing apparatus the high frequency interference picked up by said antenna, a shielding wall between said coils having an opening therein, a variable shutter movable over said opening, and an electrostatic shield between said shutter and said antenna inductance coil.

15. In a radio receiver system for a mobile craft having an ignition system radiating high frequency interference to said radio receiver system, and a storage battery common to said ignition system and said radio receiver system, said radio receiver system including a receiver circuit having tubes and a signal antenna circuit in connection with the first radio frequency stage in the receiver circuit, and means for eliminating in the signal antenna circuit the high frequency interference from the ignition system, said means including a single lead from the storage battery circuit in electrical connection with the filaments of the tubes of the radio receiver to supply the direct current of the battery thereto, a coil portion in said lead intermediate said battery and filaments inductively coupled to the signal antenna circuit, with said single lead carrying high frequency interference from the ignition system as well as direct current and with said high frequency interference acting to inductively balance out similar interference in the antenna circuit, means for varying the inductive coupling between said coil portion and antenna circuit, and an electrostatic shield intermediate said coil portion and said antenna circuit.

16. A radio receiver system including a source of operating current, an antenna circuit picking up desirable and undesirable signal impulses, a receiver circuit having translating means including current supply elements, balancing means acting to substantially prevent the introduction of said undesirable signal impulses into said translating means including a pair of coupled coils with one of said coils in connection with said antenna circuit, a single impedance free conductor from said operating current source to said second coil simultaneously carrying undesirable signal impulses and operating current thereto, a connection from said second coil to said current supply elements in said translating means to carry operating current to said elements, and means for varying the coupling between said coils.

17. In a radio receiver system for a mobile craft having a source of electrical interference thereon, a current supply for the radio receiver in said system, a signal antenna circuit for the radio receiver, with electrical interference in both said antenna circuit and said current supply and such interference being of substantially the same wave shape in each, means for eliminating in said antenna circuit said interference, said means including a single impedance free lead from said current supply to said radio receiver to supply operating current thereto, a coil in connection with said antenna circuit and with said radio receiver inductively coupled to said current supply lead, with the latter simultaneously carrying operating current and electrical interference from said current supply to inductively balance out the similar interference in said antenna circuit coil, and means for varying the inductive coupling between said coil and current supply lead.

18. A radio receiver system for a mobile craft, a power supply for said receiver, an antenna circuit for said receiver acting to pick up desirable and undesirable signal impulses, a coil in said antenna circuit, a second coil coupled to said first coil and connected to the power supply elements circuit, and a single lead from the power supply to said second coil to supply electrical power thereto and to simultaneously supply to said second coil undesirable signal impulses substantially the same as those picked up by said antenna and unaltered in wave shape in the passage to said second coil from said power supply, an apertured wall between said coils, and movable means at said aperture for varying the coupling between said coils.

RAYMOND E. WOOD. 

